If your application is in a container, then the content of the container are irrelevant to Azure, whether it is Flask, .net etc it doesn't matter.
To run it you want to use one of the services that support running containers in Azure:
- Azure Web Apps
- Azure Kubernetes Service
- Azure Container Instances
- Azure Container Apps
They all have different benefits and costs. If you want the simplest way to get started then I would look at using Azure Web Apps for containers.